1. Field of the Invention
The present invention relates generally to the field of graphics systems, and more particularly to a system and method for interactively selecting among three-dimensional objects displayed on a display screen.
2. Related Art
Graphics systems often display three-dimensional (3D) objects on display screens. Graphics systems may also allow a user to manipulate such objects being displayed. For example, a user may cause a 3D-object (e.g., a house) to be rotated at a certain angle to view the object from a different perspective. A graphics system may allow a user to manipulate multiple 3D-objects at the same time. Such a capability typically requires that the user select the objects of interest, and then specify the operation to be performed on the selected objects.
One of several schemes may be provided to enable a user to select the objects of interest. For example, a user may use a rectangle to select all the objects of interest. Typically, the user first specifies a reference position for a rectangle using a mouse button, and then drags the mouse while keeping the mouse button pressed. Dragging the mouse generally expands the rectangle. Once the mouse button is released, the objects within the expanded rectangle at the time the mouse button is released are selected.
Another scheme may use a circle instead of a rectangle. In such a scheme, the user may specify a reference position by pressing a mouse button. The reference position may correspond to the center of the circle. As the user drags the mouse, the radius of the circle may be increased: When the user releases the mouse button, all the objects within the expanded circle are selected.
Schemes such as those described above may be limited in that each of them uses a two-dimensional selection entity for selecting objects represented in three dimensional space, i.e., such selection entities do not typically include the depth dimension. The two dimensional schemes may be inadequate in certain situations. For example, a display may include several objects which are overlapping, either fully or partially. The user may wish to select objects up to only a certain depth. Two dimensional entities such as those described above may not provide the capability to select only some of the overlapping objects.
What is therefore needed is a selection entity which enables the user to select objects according to depth in addition to the two dimensions typically allowed by the two-dimension selection entities.